Add BRAIN_DISABLED flag and fix Ollama tool call formatting

Features:
  - Add BRAIN_DISABLED feature flag to hide all Brain functionality
  - When enabled, hides Brain banner, status indicator, menu, and commands
  - Flag location: src/constants/brain.ts

  Fixes:
  - Fix Ollama 400 error by properly formatting tool_calls in messages
  - Update OllamaMessage type to include tool_calls field
  - Fix Brain menu keyboard not working (add missing modes to isMenuOpen)

  UI Changes:
  - Remove "^Tab toggle mode" hint from status bar
  - Remove "ctrl+t to hide todos" hint from status bar

  Files modified:
  - src/constants/brain.ts (add BRAIN_DISABLED flag)
  - src/types/ollama.ts (add tool_calls to OllamaMessage)
  - src/providers/ollama/chat.ts (format tool_calls in messages)
  - src/tui-solid/components/header.tsx (hide Brain UI when disabled)
  - src/tui-solid/components/status-bar.tsx (remove hints)
  - src/tui-solid/components/command-menu.tsx (filter brain command)
  - src/tui-solid/components/input-area.tsx (fix isMenuOpen modes)
  - src/tui-solid/routes/session.tsx (skip brain menu when disabled)
  - src/services/brain.ts (early return when disabled)
  - src/services/chat-tui/initialize.ts (skip brain init when disabled)

src/constants/help-content.ts

@@ -89,7 +89,7 @@ export const HELP_TOPICS: HelpTopic[] = [
     fullDescription:
       "Switch between Agent (full access), Ask (read-only), and Code Review modes.",
     usage: "/mode",
-    shortcuts: ["Ctrl+Tab"],
+    shortcuts: ["Ctrl+M"],
     category: "commands",
   },
   {
@@ -166,11 +166,11 @@ export const HELP_TOPICS: HelpTopic[] = [
     category: "shortcuts",
   },
   {
-    id: "shortcut-ctrltab",
-    name: "Ctrl+Tab",
+    id: "shortcut-ctrlm",
+    name: "Ctrl+M",
     shortDescription: "Cycle modes",
     fullDescription: "Cycle through interaction modes.",
-    shortcuts: ["Ctrl+Tab"],
+    shortcuts: ["Ctrl+M"],
     category: "shortcuts",
   },
 ];